This invention generally relates to apparatus and method for removing liquid from a composition and for storing the deliquified composition and more particularly relates to an apparatus and a method for dewatering radioactive waste slurry solids, wherein the apparatus includes means for applying a vacuum to a suitable flexible filter and collapsible membrane combination in which the slurry solids are contained so that the slurry solids are compressively dewatered when the vacuum is applied and further includes means for suitably storing the resulting dewatered slurry solids.
Radioactive waste slurry solids generated by nuclear reactor power plants, governmental operations, hospitals and the like are packaged in containers for disposal at burial sites licensed by the United States government for such disposal. Often these wastes are in the form of spent ion exchange resins, filter media, waste sludge, chemical precipitates, and similar granular-type slurry media which result from water treatment processes in the facilities generating the wastes.
With particular reference to nuclear reactor power plants, a liquid moderator circulating through the reactor typically has dissolved and suspended radioactive solids therein. These solids usually are fission and corrosion products formed from within the plant piping system and plant equipment through which the moderator circulates. As well understood in the art of health physics, the radioactive liquid moderator should be kept reasonably free from such fission and corrosion products during plant operation because the radiation fields surrounding the reactor have to be maintained at a low level for biological and health reasons. Therefore, the liquid moderator is typically recirculated and filtered through ion-exchange resin beds to remove the dissolved and suspended radioactive solids. As well known in the chemical arts, an ion-exchange resin is usually a synthetic material or a natural or synthetic mineral that adsorbs an ion from solution in exchange for a less strongly held ion that previously formed part of the structure of the resin. Solid waste is deposited in the resin bed by the nuclear power plant during moderator filtering and water cleaning operations because removal of the suspended solids from the liquid moderator results in an accumulation of radioactive waste material in the resin bed. After the accumulation of radioactive material in the resin bed reaches a predetermined level, the resin is typically removed, placed into a suitable disposal container and transported to an appropriate disposal site. However, such waste, which may be in the form of spent ion-exchange resin slurry, contains a substantial amount of water and accumulated radionuclides. Moreover, some of these radionuclides may have a half-life of several hundred years and therefore should be isolated from the biosphere at least until the radiation emitting from the radionuclides has decreased to an acceptable level.
Burial of low-level radioactive wastes, such as spent ion-exchange resins, is a relatively inexpensive means for isolating the radionuclides and for providing adequate long-term shielding from the radiation emitting from the radionuclides in the wastes. However, such burial raises the possibility of leaching by water and the concomitant possibility of contamination of nearby ground water. Therefore, when burial is used as means for waste disposal, it is desirable to dewater the waste to reduce its volume and to enclose the waste in waterproof and generally leak-tight containers before burial to reduce the risk of contamination of nearby ground water.
A filter-lined container for storing hazardous solids, such as radioactive wastes, is disclosed by U.S. Pat. No. 4,058,479 issued Nov. 15, 1977, in the name of Leslie E. White, et al. entitled "Filter-Lined Container for Hazardous Solids". The White, et al. patent discloses a package for storing toxic solids in which package the stored solids are homogeneously dispersed in an immobilization material and also completely surrounded by a layer of the immobilization material. According to the White et al. patent, a tight mesh fabric bag is inserted into a barrel. The bag is filled with particulate radioactive waste material and a non-radioactive liquid that mixes with the radioactive waste material. The tight mesh of the fabric bag acts as a barrier to the solid waste, but not to the liquid. According to this patent, a portion of the liquid flows through the bag as it is filled to form a layer of non-radioactive material between the bag and the barrel wall. A substantial quantity of liquid stays inside the bag in mixture with the radioactive solids. Therefore, the White et al. patent appears to contemplate a waste container wherein the waste retains a substantial quantity of liquid. Thus, although this patent discloses a container for storing radioactive solids, this patent does not appear to disclose an apparatus and method for substantially dewatering wastes and for storing the dewatered waste in a suitable container.
An apparatus for removal of liquid from a waste burial container holding a slurry of waste material is disclosed by U.S. Pat. No. 4,582,099 issued Apr. 15, 1986, in the name of Keith K. McDaniel et al. entitled "Waste Slurry Liquid Removal System" and assigned to the Westinghouse Electric Corporation. The apparatus is provided inside a burial container and has plastic filtration tubes, which are arrayed in a multilayered configuration, extending radially from centrally located liquid withdrawal pipes. The filtration tubes have pores of a predetermined, controlled size. A combination fill head and suction head located at the opening of the container provides a system for adding waste slurry material while applying suction to one or more of the drainage layers defined by the multilayered configuration of the filtration tubes so that the liquid filtered from the slurry is removed from the container by passing through the pores of the filtration tubes. Although the McDaniel et al. patent discloses an apparatus for removal of liquid from a waste burial container, the McDaniel et al. patent does not appear to disclose an apparatus and method for dewatering wastes by compression as well as suction and for storing the dewatered wastes in a suitable container.
An apparatus and method for separating liquid-solid mixtures such as water from ion exchange resins and storing the separated out solids in a vessel are disclosed by U.S. Pat. No. 3,658,179 issued Apr. 25, 1972 in the name of Gustav Baumann entitled "Method for Separating Liquid from Solid Substances and Storing the Solid Substances". The Baumann patent discloses a self-supporting cylindrical sieve arranged in a storage vessel. A suction pipe is introduced from the top of the vessel into an annular space between the vessel wall and the sieve. The waste resin, which contains water, is caused to flow into the sieve which filters the waste allowing the filtered water to accumulate on the bottom of the vessel. The filtered water is then drained from the bottom of the vessel through the suction pipe. After the water is drained off, the remaining cavities in the waste resin and particularly the annular space between the vessel wall and the sieve are filled with a water-binding and ionizing radiation-absorbing agent such as a cement broth. The vessel is then tightly sealed for storage. Although the Baumann patent discloses an apparatus and method for separating liquid-solid mixtures, the Baumann patent does not appear to disclose an apparatus and method for dewatering wastes and for storing the dewatered wastes in a suitable container, wherein the apparatus includes means for applying a vacuum to a flexible filter and collapsible membrane combination in which the waste is contained for compressively dewatering the waste.
Consequently, although the patents recited hereinabove disclose various apparatus and methods for removing water from aqueous waste particulates or slurry, these patents do not appear to disclose an apparatus and method for deliquifying aqueous waste slurry solids, wherein the apparatus includes means for applying a vacuum to a suitable flexible filter and collapsible membrane combination for compressively deliquifying the slurry solids and further includes means for suitably storing the deliquified slurry solids.
Therefore, what is needed is an apparatus and a method for dewatering radioactive waste slurry solids, wherein the apparatus includes means for applying a vacuum to a suitable flexible filter and collapsible membrane combination in which the slurry solids are contained so that the slurry solids are compressively dewatered when the vacuum is applied and further includes means for suitably storing the resulting dewatered slurry solids.